Human induced pluripotent stem cells (iPSCs), with their potential to generate autologous patient-derived cells, hold great promise for the study and treatment of a host of devastating diseases, including Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), to name a few. One of the major obstacles slowing the translation of this powerful technology to the clinic is the heterogeneity of both desired and unwanted cell types generated in grafts of iPSCs, even after cells have been directed down specific differentiation pathways. Similarly in culture, a multitude of cell types are generated after treatment of iPSCs with lineage-specifying cocktails. These realities, combined with the current lack of suitable cell surface markers for the selection of specific desired cell types, has significantly impacted the field, hampering our ability to develop cell replacement therapies or to accurately model diseases in the dish. One plausible explanation for the observed cell heterogeneity is that presumptive undifferentiated pluripotent cells sometimes spontaneously initiate the process of differentiation after encountering lineage- specifying cues in culture, thereby precluding their subsequent directed differentiation by exogenously added differentiation cocktails. Currently, there are no assured ways to know if iPSCs have begun to spontaneously differentiate. However, an exciting new discovery made during our previous grant cycle suggests that the epigenetic state of chromatin shortly after DNA replication serves as a reliable and very early indicator of the state of differentiation of a stem cell. Our results suggest that it may be possible to uniformly direct the differentiation of all iPSCs toward a specific cell fate if chromatin can be kept closed until incubation with exogenous fate-specifying differentiation factors. If these insights are indicative of a more generalized principle, then it should be possible to generate pure populations of neural progenitors (NPs) of different subtypes which can give rise to homogeneous populations of various neurons for studies in culture and in animal models of multiple diseases. With these goals in mind, our Specific Aims for this proposal are: 1) to assess chromatin status during commitment to a motor neuron phenotype; 2) to generate pure populations of midbrain dopamine (mDA) and motor NPs and neurons which will be characterized for phenotype and synaptic function in culture and 3) to further determine whether homogeneous mDA-committed NPs/neurons can accurately model PD in the dish and be used in transplants to therapeutically treat PD rat models.